516 Paul Thompson
generated. This adaptive landscape is a three dimensional phase space (a system
with a larger number of loci will have a correspondingly larger dimensionality):
W
p 1p 2The plotted point is the average fitness of the population described above. A
complete adaptive landscape is a surface with adaptive peaks and valleys. An
actual population under selection may climb a slope to an adaptive peak that is
sub maximal (i.e., the average fitness of the population is less than the highest
average fitness in the system). The only way to move to another slope which
leads to a more maximal or maximal average fitness is to descend from the peak.
This involves evolving in a direction of reduced average fitness that is opposed by
stabilizing selection. Hence, the population is stuck on the peak at a sub maximal
average fitness. When several populations are on different sub-maximal average
fitness peaks, selection between populations (interdemic selection) can act.
This population genetic description has been used extensively to explain situ-
ations which cannot be explained in terms of intrademic selection. For example,
body size which may have high individual fitness, and hence is selected for within
a population, can reduce the fitness of the population by causing it to achieve a
sub maximal average fitness and leave it open to interdemic selection.
3.3 Formalisation in Ecology
Over the last 40 years, ecology has acquired remarkable theoretical depth. Al-
though the extensive empirical research undertaken during this period has provided
the fuel for, and substantiation of, the theoretical advances, it is the vigorous em-
ployment of mathematical modelling that is largely responsible for its theoretical
richness and the uncovering of complex mechanisms underlying an initially be-
wildering complexity. Ecology is a large domain of empirical investigation, which
makes a comprehensive formalisation exceedingly complex. A comprehensive for-
malisation is in principle possible but is seldom employed in practice. Different
aspects of ecological dynamics are usually formalised, and employed, separately
since this provides the most useful framework for exploring the dynamics and di-
recting empirical research. I provide, as an illustration, a sketch of a couple of the
foundational features of ecological modelling.